1. Field of the Invention
This invention relates to a hand-held controllable power injector as applied to syringes adopted to deliver a liquid into a patient. More particularly, the invention relates to a hand-held controllable power injector for delivering, by injection, x-ray contrast media into a patient prior to or during urographic or angiographic procedures.
In a particular embodiment the invention relates to an engagement feature between the syringe and the power assistor which prevents inadvertent activation of the power assistor and the consequent undesired expulsion of the liquid from the syringe.
2. Reported Developments
Urography is a radiological technique wherein at least a part of the urinary tract of a mammal is rendered opaque by intravenous injection of a contrast medium or by injection into the bladder through the urethra.
Angiography is also a radiological technique wherein the arteries or veins of a mammal are outlined by injecting a radiographic medium.
In both techniques the coated vascular structures are radiographically imaged for diagnostic purposes.
For delivery to the desired site, the contrast medium is placed in an appropriate syringe and forced through a hollow needle or a catheter in such a manner that the contrast medium enters the blood stream or the bladder at the appropriate time and place for taking radiographic images. As contrast medium is being injected to the site to be visualized through the hollow needle or a catheter, high pressures are often encountered, sometimes as high as 1,000 psi. This requires a rather high force to be exerted on the piston in order to deliver the content of the syringe. Furthermore, such force is to be exerted in a constant manner for continuous and even volume delivery of the contrast medium. Early injection systems were designed for manual injection of the contrast medium by means of a hand-held glass syringe. A mechanical injection system activated by a foot switch has also been, and is still being used for most general radiographic procedures. However, this system was only rarely used for coronary angiography for the probable reason that operator control is greatly reduced and the risk of coronary artery dissection increased.
Power injectors in general have certain advantages over hand-operated injectors including the following. They reduce reliance on an assistant enabling the operator to be in complete control of the injection of the contrast medium, they can deliver a precise volume, and the pressure generated can be limited by presetting a pressure limit.
Power injectors are of three types: hydraulic, pneumatic and electric. Hydraulic injectors have an electric motor connected to a hydraulic pump, which drives a ram connected to a syringe that contains the contrast medium. In pneumatic injectors, the source of power is compressed gas supplied by a tank or compressor. Electric injectors are powered by electric motors in which a transmission means serves to change circular motion into linear motion which then drives a ram.
While typical power injectors eliminate the physical effort required with manual injectors, they are not easy to use, are expensive and the perception of instantaneous control present with manual injectors is lost because the syringe and controls for the injectors are not hand-held or not conveniently handleable during the injection process. For example, a gas power-injector hand-held syringe does eliminate the physical effort associated with manual injection and also provides a perceived instantaneous control of the injection, however, it requires a gas system to power the syringe, such as pressurized carbon dioxide gas. The gas delivery system includes a carbon dioxide gas tank with various indicators and controls, which reduces the portability of the device, it requires valuable space in the proximity of the injection, it adds to the complexity of using the device for the intended purpose and requires periodic replacement of the gas tank.
Battery powdered injectors are also available for use in angiography and urography employing a syringe for holding a contrast medium and a plunger connected to a mechanical means to automatically deliver the contrast medium. Some of these injectors include microprocessor technology for programming rates and time delivery and have visual or audio display for ease of controlling the injection process. As these injectors become more sophisticated, the cost of making and using them increases as well as the complexity of use tends to increase the opportunities for breakdown.
The present invention is directed to a hand-held, light-weight power injector which eliminates the physical effort required with manual injectors but otherwise allows the practitioner complete human control of the injection process.